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Method and apparatus for generating a localized heating


Title: Method and apparatus for generating a localized heating.
Abstract: A method and apparatus for generating a localized heating are provided, the method comprising: transmitting a spatially localized or shaped electromagnetic field via a plurality of coils to a subject and generating magnetic resonance signals; performing magnetic resonance imaging based on the magnetic resonance signals to generate an image of a region of interest of the subject; and controlling the plurality of the same imaging coils to radiate radio frequency (rf) energy to generate the localized heating on a region of interest. The invention provide a more efficient manner for generating localized heating and means for verifying the heating pattern without the need to measure temperature rises in the patient. This is useful to check the localization prior to the application of hyperthermia. ...

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USPTO Applicaton #: #20100145420 - Class: $ApplicationNatlClass (USPTO) -
Inventors: Yudong Zhu, Thomas Kwok-fah Foo



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The Patent Description & Claims data below is from USPTO Patent Application 20100145420, Method and apparatus for generating a localized heating.

FIELD OF THE INVENTION

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The subject matter disclosed herein relates generally to a method and an apparatus for generating a localized heating, and more particularly, to a method and an apparatus for generating a localized heating on a region of interest of a subject by a magnetic resonance imaging (MRI) system.

RELATED ART

In the field of oncology, hyperthermia is frequently used in conjunction with chemotherapy to improve an efficiency of tumor cell killing. Radio frequency (RF) hyperthermia is a standard tool in the oncology field to generate spatially controlled (localized) heating patterns within a body. Conventional RF hyperthermia uses an array of dipole antennas placed around the body and delivers the necessary energy via a continuous or pulsed RF waveform.

An amplitude and a phase of the RF waveform at each element is varied to provide the necessary spatial localization. Verification of the localized heating pattern is performed via invasive thermocouples that directly measure the temperature rise or non-invasively using MR or infrared thermometry. In addition, to improve the efficiency of delivering the RF energy to the patient, a water-filled bag surrounding the patient is used to increase the coupling of the RF to the body.

MR thermometry, using proton resonance frequency (PRF) shifts, has been used with RF hyperthermia to monitor the heating pattern and to adjust the application of RF energy so as to target only the region of interest (e.g., Kowalski M E, et al, IEEE Trans Biomed Eng 2002; 49: 1229-41). However, cumbersome water-filled bags are used and the heating pattern is adjusted and verified based on the image-based thermometry data. Therefore, an improved method and apparatus for generating a localized heating in a region of interest of a subject overcoming foregoing disadvantages is desired.

SUMMARY

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OF THE INVENTION

In a first aspect, a method for generating a localized heating is provided. The method includes the steps of: transmitting a spatially localized or shaped electromagnetic field via a plurality of coils to a subject and generating magnetic resonance signals; performing magnetic resonance imaging based on the magnetic resonance signals to generate an image of a region of interest of the subject; and controlling the plurality of the coils to radiate radio frequency (rf) energy to generate the localized heating in a region of interest.

In a second aspect, an apparatus for generating localized heating is provided. The apparatus includes: a plurality of coils configured to transmit a spatially localized or shaped electromagnetic field to a subject and to generate magnetic resonance signals; an imaging device configured to perform magnetic resonance imaging based on the magnetic resonance signals to generate an image of a region of interest of the subject; and a control device configured to control the plurality of the coils to radiate RF energy to generate the localized heating on the region of interest.

In a third aspect, a method for generating a localized heating is provided. The method includes: transmitting radio frequency energy via a plurality of coils to a subject; and generating unique radio frequency waveforms on each of the coils to generate an arbitrary specific absorption rate distribution in the subject to enable spatially localized heating.

In a fourth aspect, a method for generating a localized heating pattern and imaging is provided. The method and apparatus includes: a plurality of coils configured to transmit a spatially localized or shaped time-varying magnetic field to excite spins of interest within the body to generate magnetic resonance signals. Furthermore, the same configuration of coils is used to also transmit a spatially localized or shaped electric field to generate an arbitrary specific absorption rate distribution in the subject to enable spatial localized heating.

BRIEF DESCRIPTION OF THE DRAWINGS

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The features and advantages of the invention will become apparent from the following detailed description of the embodiments of the invention when read with the accompanying drawings in which:

FIG. 1 illustrates a block diagram of a system for generating a localized heating in accordance with certain embodiments of the invention.

FIG. 2 is a simplified block diagram showing a linear coil array in accordance with one embodiment of the invention.

FIG. 3 is a simplified block diagram showing a coil array in accordance with another embodiment of the invention.

FIG. 4 is a flow chart showing operation of an apparatus in accordance with one embodiment of the invention.

FIG. 5 illustrates a simplified block diagram of the apparatus for generating a localized heating in accordance with another embodiment of the invention.

FIG. 6 is a flow chart of a method in accordance with one embodiment of the invention;

FIG. 7 shows the specific absorption rate (SAR) pattern by using a conventional sinusoidal distribution of current in a quadrature body coil.

FIG. 8 shows SAR pattern by using an 8-channel parallel coil and a choice of coil weights {wme}.

DETAILED DESCRIPTION

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The embodiments of the invention will be described in detail with respect to the figures below. Taking into account that detailed description of some related art would confuse the invention, the detailed description thereof will not be provided herein. In the drawings, the same reference numerals are used to indicate the same elements or components performing the same functions.

FIG. 1 illustrates a block diagram of a system for generating the localized heating in accordance with embodiments of the invention. The system is an MR imaging system that incorporates the embodiments of the invention. The MRI system could be, for example, a GE-Signa MR scanner available from GE Medical Systems, Inc., which is adapted to perform the method of the invention, although other systems could be used as well.

The operation of the system is controlled from an operator console 100 which includes a keyboard and control panel 102 and a display 104. The console 100 communicates through a link 116 with a separate computer system 120 that enables an operator to control the production and display of images on the screen 104. The computer system 120 includes a number of modules which communicate with each other through a backplane. These modules include an image processor module 106, a CPU module 108, and a memory module 113, known in the art as a frame buffer for storing image data arrays. The computer system 120 is linked to disk storage 111 and tape drive 112 for storage of image data and programs, and it communicates with a separate system control 122 through a high speed serial link 115.

The system control 122 includes a set of modules connected together by a backplane. These modules include a CPU module 119 and a pulse generator module 121 which connects to the operator console 100 through a serial link 125. It is through this link 125 that the system control 122 receives commands from the operator which indicate operations that are to be performed. The pulse generator module 121 operates the system components to carry out the desired operations. It produces data that indicate the timing, strength, and shape of the radio frequency (RF) pulses which are to be produced, and the timing of and length of the data acquisition window. The pulse generator module 121 connects to a set of gradient amplifiers 127, to indicate the timing and shape of the gradient pulses to be produced during the scan. The pulse generator module 121 also receives subject data from a physiological acquisition controller 129 that receives signals from a number of different sensors connected to the subject 200, such as ECG signals from electrodes or respiratory signals from a bellows. And finally, the pulse generator module 121 connects to a scan room interface circuit 133 which receives signals from various sensors associated with the condition of the subject 200 and the magnet system. It is also through the scan room interface circuit 133 that a positioning device 134 receives commands to move the subject 200 to the desired position for the scan.

The gradient waveforms produced by the pulse generator module 121 are applied to a gradient amplifier system 127 comprised of Gx, Gy and Gz amplifiers. Each gradient amplifier excites a corresponding gradient coil in an assembly 139 generally designated to produce the magnetic field gradients used for position encoding acquired signals. The gradient coil assembly 139 forms a part of a magnet assembly 141 which includes a polarizing magnet 140 and a RF coil system 152. Volume 142 is shown as the area within magnet assembly 141 for receiving subject 200 and includes a patient bore. As used herein, the usable volume of a MRI scanner is defined generally as the volume within volume 142 that is a contiguous area inside the patient bore where homogeneity of main, gradient and RF fields are within known, acceptable ranges for imaging. A transceiver module 150 in the system control 122 produces pulses that are amplified by a RF amplifier system 151 and coupled to the RF coil system 152 by a transmit/receive switch system 154. The resulting signals radiated by the excited nuclei in the subject 200 can be sensed by the same RF coil system 152 and coupled through the transmit/receive switch system 154 to a preamplifier system 153. The amplified MR signals are demodulated, filtered, and digitized in the receiver section of the transceiver 150. The transmit/receive switch 154 is controlled by a signal from the pulse generator module 121 to electrically connect the RF amplifier system 151 to the coil system 152 during the transmit mode (i.e., during excitation) and to connect the preamplifier system 153 during the receive mode. The transmit/receive switch system 154 also enables a separate RF coil (not shown, for example, a head coil or surface coil) to be used in either the transmit mode or the receive mode.

In the embodiments of the invention, the RF coil system 152 is a transmit/receive coil array assembly that will be described with reference to FIGS. 2-3. During the transmit mode, the RF pulse waveforms produced by the pulse generator module 121 are applied to a RF amplifier system 151 comprised of multiple amplifiers. Each amplifier controls the current in a corresponding component coil of the coil system 152 in accordance with the amplifier's input RF pulse waveform. With the transmit/receive switch system 154, the RF coil system 152 is configured to perform transmission and reception simultaneously or alternatively.

As used herein “adapted to”, “configured” and the like refer to mechanical or structural connections between elements to allow the elements to cooperate to provide a described effect; these terms also refer to operation capabilities of electrical elements such as analog or digital computers or application specific devices such as an application specific integrated circuit (ASIC) that is programmed to perform a sequence to provide an output in response to given input signals.

The MR signals picked up by the RF coil system 152 or a separate receive coil are digitized by the transceiver module 150 and transferred to a memory module 160 in the system control 122. When the scan is completed and an entire array of data has been acquired in the memory module 160, an array processor 161 operates to Fourier transform the data into an array of image data. These image data are conveyed through the serial link 115 to the computer system 120 where they are stored in the disk memory 111. In response to commands received from the operator console 100, these image data may be processed by the image processor 106 and conveyed to the operator console 100 and presented on the display 104, or they may be further archived on the tape drive 112. Further processing is performed by the image processor 106 that includes reconstructing acquired MR image data.

Referring to FIG. 2, in one embodiment, a transmit/receive coil array assembly 300 for use in the embodiment of the invention comprises a plurality of radio frequency (rf) coils 210 configured for transmitting in parallel during transmission mode and a plurality of RF amplifiers 220 coupled to the corresponding RF coils adapted to generate a controlled current in each of the RF coils, and wherein the controlled current being used for defining and steering a region of interest 230 of the subject 200 within the system. In FIG. 2, the placement of the coils is substantially linear.

Referring to FIG. 3, an alternative embodiment is shown, in which RF coils 210 are arranged in an equally distributed pattern about the subject 200, such as a circle.

Hereinafter, the embodiments of the invention will be further described in details in conjunction with the drawings.

FIG. 4 is a flow chart showing the operations of the apparatus in accordance with one embodiment of the invention.

As shown in FIG. 4, the apparatus of the embodiment of the invention is used to generate the localized heating based on the magnetic resonance imaging (MRI). After the operation is started, in Step 402, a spatially localized or shaped electromagnetic field is transmitted to the subject 200 and magnetic resonance (MR) signals are generated through a plurality of coils. Specifically, the pulse generator module 121 produces the RF pulse waveforms, and applies the RF pulse waveforms to the RF amplifier system 151 comprised of multiple amplifiers which control the current in each component coil of the coil system 152, which comprises a plurality of coils 210 as shown in FIGS. 2 and 3, in accordance with the amplifier's input RF pulse waveform, so that the coil system 152 transmits the electromagnetic field to the subject 200 and generates MR signals.

Then, in Step 404, the MR imaging is performed based on the MR signals to generate image of a region of interest 230 of the subject 200. Specifically, the coil system 152 picks up the MR signals. With the transmit/receive switch system 154, the MR signals picked up by the coil system 152 are digitized by the transceiver module 150 and transferred to a memory module 160 of the system control 122.

When an entire array of data has been acquired in the memory module 160, an array processor 161 operates to Fourier transform the data into an array of image data. These image data are conveyed through the serial link 115 to the computer system 120 where they are stored in the disk memory 111. In response to commands received from the operator console 100, or automatically, these image data are further processed by the image processor 106 and conveyed to the operator console 100 and presented on the display 104. In addition, these image data may also be archived on the tape drive 112. Here, the image processor 106 performs MR imaging based on the MR signals to generate image of the region of interest 230 of the subject 200.

Then, in Step 406, the plurality of coils 210 are controlled to radiate radio frequency energy via a RF waveform to generate localized heating in the region of interest 230. Specifically, the pulse generator 121 and the coil system 152 are controlled by the CPU module 108 and/or the CPU module 119 to radiate radio frequency energy via the RF pulse waveform to generate localized heating within a range of the region of interest 230 based on the image of the region of interest 230.

Implicit in the preceding description of the work flow is the incorporation of a calibration step wherein the B1 field distribution for each of the coil elements 210 in the multiple element coil array is measured. This information is used to compute the radio frequency amplitudes and phase for each coil element in order to generate the appropriate distribution of the electric field in the subject 240, and consequently, the heating or specific absorption rate distribution in the subject 240.

In one embodiment, a localized heating is generated by the apparatus of the embodiment of the invention based on the electromagnetic field. Specifically, a set of weights (radio frequency coil amplitude and phase for each coil element 210) are calculated by CPU 108 or 119 such that the magnitude of the magnetic field equals that of a desired magnetic field within the region of interest 230. A magnetic field excitation pattern that can be observed in the image is generated by means of the radio frequency energy based on the set of weights. The corresponding radio frequency electric field distribution is inferred by comparing the radio frequency magnetic field excitation pattern in the image. Then, the spatially localized heating pattern is predicted by the inferred radio frequency electric field distribution. The localized heating pattern can also be generated by using unique radio frequency (rf) waveforms in each of the plurality of coils 210 and/or simultaneously adjusting the amplitude and phase of the unique radio frequency waveforms. In either case, the individual coil element weights (amplitude and phase) that results in a desired localized heating pattern or distribution will also yield a unique magnetic (B1) field excitation pattern that can be visualized in a magnetic resonance image. The heating pattern (electric field distribution) then corresponds to the MR B1-field excitation pattern. In one embodiment, the unique radio frequency waveform is a unit radio frequency sinusoidal pulse. The use of other waveforms will also yield similar results.

In other words, a set of weights (amplitude and phase of each coil element 210) are calculated by CPU 108 or 119 such that the magnitude of the magnetic field equals that of a desired magnetic field within the region of interest 230, an electric field is generated by the plurality of coils based on the same set of weights, and the localized heating is generated by the apparatus based on the applied electromagnetic field with the same set of computed weights.

Specifically, the above procedure will be further described in detail as below.

The embodiment of the invention is based on the parallel transmit technique that was originally intended to provide a more homogeneous transmit B1-field (B1+) and also to reduce the overall SAR. Note that

S   A   R = 1 2  σ   E  2 ( 1 )


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stats Patent Info
Application #
US 20100145420 A1
Publish Date
06/10/2010
Document #
12328444
File Date
12/04/2008
USPTO Class
607103
Other USPTO Classes
600411
International Class
/
Drawings
7


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